1. Assessment Of Defects In Concrete Structures And
Evaluation Of Safety Of Concrete Infrastructure
Training
4th Day
Rehabilitation methods and Strengthening Techniques
By:
MAHMOUD ABUFOUDA
MSc Civil Engineer
2. Content
Rehabilitation
Methods
•Repair using mortars.
•Dry pack
•Pre-placed aggregate concrete (PAC)
•Self Compacted Concrete (SCC)
•Epoxy bonded concrete
•Polymer concrete system
•Protective seal coats
•Plate bonding
•Section enlargement
•Propping and supporting
•Fiber Reinforced Polymers (FRPs)
Strengthening
Techniques
• The need for strengthening
• Flexural Strengthen of Beams
• Shear Strengthening of Beams
• Strengthening of Columns
3. Rehabilitation/Repair Methods
Various methods are available
Single or combination of methods can be used according to the assessment of
the distress.
The basic methods are;
1. Repair using mortars.
2. Dry pack
3. Pre-placed aggregate concrete (PAC)
4. Concrete replacement
5. Shotcrete
6. Self Compacted Concrete (SCC)
7. Epoxy bonded concrete
8. Silica fume concrete
9. Polymer concrete system
4. Rehabilitation/Repair Methods
10. Thin polymer overlays
11. Thin epoxy overlay
12. Protective seal coats
13. Ferro-cement
14. Plate bonding
15. Section enlargement
16. Propping and supporting
17. Fiber Reinforced Polymers (FRPs)
18. Chemical and electro-chemical methods
5. Repair Methods- Repair with Mortars
It is the most common form of repair.
Types of mortar repairs;
1. Portland cement mortars
2. Polymer modified cement mortars
3. Epoxy mortars
6. Repair Methods-Portland Cement Mortars
Applied for cosmetic and very small superficial repair areas not associated
with critical performance of the structure.
Shall not be used for repairs to old or existing concrete
Shall not be used for repairs that extend to or below the first layer of
reinforcing concrete.
It is advisable to use the same proportion of cement: sand: water as used in
the preparation of parent concrete.
Portland cement mortars need to be cured
7. Repair Methods-Modified Cement Mortar
Used only for repairing defects on exposed concrete surface.
Has higher performance properties than normal cement (Fast setting,
strength, etc.).
For larger repair areas with thickness in excess of 50 mm. concrete is for
thicker thickness.
For larger areas, it is advisable to use steel reinforcing mesh fixed with nails.
8. Repair Methods-Epoxy Mortars
Depending on the type, epoxy mortars consist of resin, hardener and silica
sand.
Applied over the epoxy bonding coat over the hardened concrete surface.
It attain strength within few hours.
High strength, Water resistant and Abrasion resistant.
Can be used in few millimeter thickness.
10. Repair Methods- (PAC)
Preplaced aggregate concrete is made by forcing the grout into the voids of
mass of clean graded coarse aggregate pre-packed in the form work.
The grout consists of sand, cement, pozzolana, plasticiser/superplasticiser
and air entraining agents.
https://www.youtube.com/watch?v=T9r6Cwj5Ehs
https://www.youtube.com/watch?v=BmvmIUK1w
AY
11. Repair Methods- Concrete replacement
Concrete replacement shall be used. If the area of damaged or unacceptable
concrete is
greater than 0.1 sqm and
having a depth of more than 150 mm or
extending 25 mm from the back side of the reinforcement.
Epoxy agents, latex bonding agents, dry neat cement, cement paste or
cement and sand mortars shall not be used to bond.
Normally the concrete used should have a modified properties agents such as
superplasticier to enhance workability.
Not efficient (has segregations, honeycomb problems, etc.).
12. Repair Methods-Self-Compacted Conc.
The use of SCC in renovation works is a natural result of its fabulous
characteristics.
SCC can solve many constructability and placement challenges that most
concrete mix designs cannot like
Consolidates under its own weight.
Pumping and placement into very congested formwork and reinforcing bars.
Doesn’t need mechanical compaction.
The main feature of this unique type of concrete relates to having very high
slump and flowability properties without segregation.
https://www.youtube.com/watch?v=YH42V9yyGZg
https://www.youtube.com/watch?v=jHUQCbakzXE
13. Repair Methods- Shotcrete
Shotcrete is defined as pneumatically applied concrete or mortar placed
directly onto a surface.
It is one of the oldest materials and the most common techniques of repairing
and strengthening of reinforced concrete structures.
Sprayed concrete has been used in that field for almost 90 years.
Shotcrete shall be placed by either the dry mix or wet mix process.
Dry mix sprayed concrete in which most of the mixing water is added at the nozzle
Wet mix sprayed concrete in which the ingredients , including water, are mixed
before introduction into the delivery hose.
Both are used in concrete repair/strengthening work, but the use of dry mix
sprayed concrete is more common.
16. Repair Methods- Polymer Concrete
Like Methyl Methacrylate (MMA) Polymer Concrete.
Used for patches, overlays, grout pads and embedment of slits, gates and
similar structures in concrete members.
The physical properties (e.g. compressive, tensile, flexural strength and
modulus of elasticity) of cured repaired materials are very high.
https://www.youtube.com/watch?v=lDvKpzP2Rug&feature=youtu.be
17. Repair Methods- Silica Fume Concrete
Silica fume concrete is a mix of Portland cement and silica fume which is used
as effective Pozzolana material in quantities that is not exceeding 10% by the
weight of cement in the concrete mix.
This mix shall be used with superplasticizer.
It may be used where a high strength repair concrete of low permeability is
required
18. Repair Methods- Epoxy bonded concrete
It is defined as freshly mixed Portland cement concrete that is placed over
epoxy resin bond coat on existing hardened concrete.
Mostly, it is concrete-concrete epoxy types.
Usually, it is mixed with silica sands materials.
Used to bond new layer of concrete with the parent concrete.
In case of a deep concrete casting, anchors and fasteners should be used with
this type of repair to ensure the bonding between new concrete and parent
one.
19. Repair Methods- Ferrocement
Ferrocement can be described as a type of thin
composite material made of cement mortar
reinforced with wire meshes.
The steps;
removing the concrete from the cracked affected zone.
layer of galvanized welded wire mesh and a layer of
skeletal steel are fixed with the original reinforcement
of the slab.
concrete surface must roughened before the additional
reinforcement is placed
additional reinforcement result from the design and
technological restrictions are added.
Polymer modified Concrete is applied.
20. Repair Methods- Protective Sealcoats
Seal coats are defined as liquid epoxy that are applied to the surface of
hardened concrete to prevent or decrease the penetration of liquid or
gaseous media.
https://www.youtube.com/watch?v=wBeUWXvK0nU
21. Repair Method-Cracks Epoxy Injections
This technique used to treat the cracks in concrete by injecting epoxy into
the cracks.
The process is illustrated in this video
https://www.youtube.com/watch?v=7_diXmKZp_8
22. Repair Methods- Plate Bonding
Inexpensive, multi-functional and advanced technique for rehabilitation.
It consists in bonding steel plates or steel flat bars to the structural elements
by steel bolts and epoxy.
Substantially increase the stiffness, ductility and stability.
24. Repair Methods- Section Enlargement
On of the traditional techniques in the rehabilitation of reinforced concrete
structures.
This technique aims to increase the structural cross section area of the
structure elements.
Can be apply to all structural elements ( slabs, beams, columns, foundation,
etc.
The type of bonding is a critical factor in this type of technique.
25. Repairing Methods- Fiber Reinforced Polymers
(FRPs)
Fiber Reinforced Polymer system is a patented cost effective family of well
proven & engineered, strengthening products designed to meet a wide variety
of strengthening applications on concrete.
FRP materials have superior properties with respect to strength, weight,
durability, creep, and fatigue.
The current commercially available FRP reinforcements are
1. Continuous fibers of aramid (AFRP).
2. Carbon (CFRP).
3. Glass (GFRP) impregnated in a resin matrix.
26. Repairing Methods- Fiber Reinforced Polymers
(FRPs)
Applications
Seismic
Retrofitting
Structural
Upgrades
Structural
Repairs
Design or
Construction
Errors
Blast
Mitigation
Modifications
to Structural
Elements
Corrosion
Repairs
Load
Increases
Underwater
Repairs
27. Repairing Methods- Fiber Reinforced Polymers
(FRPs)
FRP composites can be produced by different manufacturing methods in many
shapes and forms.
Rods (bars): used for internal concrete reinforcement.
Pre-cured laminates Plates : used to replace bonded steel plates.
Pre-cured laminate shells: used as jackets for columns.
Fiber sheets: commonly used for external concrete reinforcement
28. Strengthening of RC Elements
The aim of strengthening is to increase the capacity of an existing structural
element.
Strengthening can be achieved by:
Replacing poor quality or defective material by better quality material
Attaching additional load-bearing material
Redistribution of the loading actions through imposed deformation of the structural
system
29. Strengthening of RC Elements
The new load-bearing material:
Load-
bearing
material
High quality
concrete
•SCC
•UHPC (Ultra High
Performance
Concrete)
•Polymer Modified
Concrete
Reinforcing steel
bars
Thin steel plates
and straps
Post-tensioning
tendons
Using Composite
elements such as
Steel W sections
FRP composite
materials
•CFRP
•AFRP
•GFRP
30. Strengthening of RC Elements
The need of structural strengthening
Load increases
due to:
• Higher live loads,
• Increased wheel
loads,
• Installations of
heavy machinery
• Vibrations
Damage to
structural parts
due to:
• Aging of
construction
materials
• Fire damage,
• Corrosion of
steel
reinforcement
• Impact of
vehicles
Improvements in
suitability for use
due to:
• Limitation of
deflections,
• Reduction of
stress in
reinforcement
• Reduction of
crack widths
Modification of
structural system
due to:
• Elimination of
walls/columns
• Openings cut
through slabs
Errors in planning
or construction
due to:
• Insufficient
design
dimensions
• Insufficient
reinforcing steel
31. Strengthening of RC Elements
The following slides will discuss
1. Flexural Strengthening of RC Beams.
2. Shear Strengthening of RC Beams.
3. Strengthening of RC Columns.
32. Flexural Strengthening of RC Beams
In most cases, the compression zone of RC beam is safer from failure as the
tension zone if it is under pure bending.
The critical area for beam under bending stresses is a tension zone of the RC
beam.
Mostly, the failure initiated by the development of crack from tension zone,
and extended up to compression zone before reaching to failure.
These cracks usually start from the bottom of applied load, which indicates
flexural failure.
33. Flexural Strengthening of RC Beams
There are several Flexural strengthening techniques for RC beams.
Section enlargement
Ferrocement cover
External plate bonding
External post-tensioning
Fiber Reinforced Polymer (FRPs)
•Prefabricated laminates
•Near Surface Mounted bars NSM
34. Section Enlargement
Section enlargement is one of the famous methods used in retrofitting
concrete members.
Section enlargement maybe easier and cheaper compared to other
approaches.
Enlargement consists of the placement of reinforced concrete jacket around
the existing structural member to achieve the desired section properties and
performance.
35. Section Enlargement
• Increasing of the load-
carrying capacity
• Increasing of the
stiffness
• Increase in the
concrete member size
obtained after the
jacket
• Increasing loads to be
attained by other
elements
• The need to construct
a new formwork
Advantages
Disadvantages
36. Section Enlargement
There are two different scenarios for Strengthening RC beams by section
Enlargement;
1. Enhancing negative moment capacity by adding new reinforcement and new
concrete layer to the bottom face of the structural beam.
2. Enhancing positive moment capacity by adding new reinforcement and new
concrete layer to the top face of the structural beam.
In this technique the most important problem is to ensure an appropriate
bonding between “old” concrete in the existing structure and “new” concrete
applied for strengthening the structure.
37. Formwork and
applying of the
repair material
Reinforcement
protection (in some
cases)
Replacement or
addition of the
supplementary
reinforcement
Surfaces cleaning
and preparation to
ensure bonding
with the repair
material
Corrosion removal
from the exposed
reinforcement
Removal of the
deteriorated
concrete
Temporary
supports
Section Enlargement
Steps to perform section enlargement techniques for RC beams;
https://www.youtube.com/watch?v=zkaMGT2b1ck (Steps)
https://www.youtube.com/watch?v=xDQnJ1iFTNA
38. Ferrocement Cover
Thin composite material made of cement mortar reinforced with wire
meshes.
The wire meshes are uniformly distributed in continuous layers with relatively
small diameters.
The Ferro cement is used to replace the damaged concrete.
Strengthening with Ferro cement improves:
Cracking resistance
Flexural stiffness
The ultimate loads compared to the original un-strengthened element.
These improvements depend on the full composite action between the Ferro
cement layers.
39. External Plate Bonding
Steel plates or steel flat bars are bonded to the structural elements.
Widely appear in strengthening of bridge structures.
The bonding is ensured by:
The use of epoxy adhesives,
Additional fastening by means of dowels or bolts glued to the holes drilled in the
concrete members.
Disadvantages: it can be applied only to the relatively sound structures
40. External Plate Bonding
Attaching the
steel plates to
the concrete
using bolts
Putting a layer
of epoxy mortar
on top of the
plates with a
5mm thickness.
Making holes in
the concrete
surfaces and
plates.
Coating the
concrete
surfaces with a
bonding epoxy
material.
Roughing and
cleaning the
concrete
surfaces where
the plates will
be attached.
41. External Post-Tensioning
Effective in increasing the flexural and shear capacity.
Applied to reinforced and prestressed concrete members.
The post-tensioning forces are delivered by:
Standard pre-stressing tendons
High-strength steel rods
Usually located outside the original section.
The repair system supplements minimal additional load to the structure thus
being an effective economical strengthening technique.
42. External Post-Tensioning
https://www.youtube.com/watch?v=4nApm5nLUh8
The tendons are
connected to the
structure at anchor
points, typically
located at the ends
of the member
The existing cracks
must be repaired by
means of epoxy
injecting or other
known methods
If there are existing
spalls patching must
be done, because
this repairs must
ensure that the pre-
stressing forces are
distributed uniformly
across the section of
the member
43. Fiber Reinforced Polymer (FRP)
FRP
High Strength
• ×5 Steel
Multifunction
al
•Suit any
project
Corrosion
Resistance
•Durable
Structure
Light Weight
•Easy to install
44. Fiber Reinforced Polymer (FRP)
FRP is a new class of composite material for the development and repair of
new and deteriorating structures in Civil Engineering.
FRPs are organized in a laminate structure.
each lamina (flat layer) contains an arrangement of unidirectional fibers
fabrics embedded within a thin layer of light polymer matrix material.
FRP consists of two main components:
Fibers.
Resin or Matrix.
60. Shear Strengthening of RC beams
Shear failure is a sudden failure which make it more devastating than the
Flexural failure.
Shear failure start occurring from the critical section at high shear zone near
support.
The failure is usually occurring without giving any alarming alerts.
Shear force maximum at support and the diagonal cracks start from support
to applied load.
These diagonal cracks formed on either side or both sides together in RC
beam and failure occurred by widen of shear cracks in RC beam
62. Strengthening of RC Columns
Strengthening of reinforced concrete columns is needed when:
The load carried by the column is increased due to either increasing the number of
floors or due to mistakes in the design.
The compressive strength of the concrete or the percent and type of
reinforcement are not according to the codes’ requirements.
The inclination of the column is more than the allowable.
The settlement in the foundation is more than the allowable.
There are many techniques for strengthening RC columns, the most famous
techniques are:
1. RC jacketing
2. Steal Jacketing
3. Using FRP wraps
63. Strengthening of RC Columns- RC jacket
The size of the jacket and the number and diameter of the steel bars used in
the jacketing process depend on the structural analysis that was made to the
column.
The loads applied to the column shall be reduced or eliminated by:
Putting mechanical jacks between floors.
Putting additional props between floors.
In case of corrosion in Reinforcement;
1. Remove the concrete cover.
2. Clean the steel bars using a wire brush or sand compressor.
3. Coat the steel bars with an epoxy material that would prevent corrosion.
https://www.youtube.com/watch?v=aXP4oNzi6YM
65. Strengthening of Columns- Steel jacket
This technique is chosen when the loads applied to the column will be
increased, and at the same time, increasing the cross sectional area of the
column is not permitted.
67. Strengthen RC Columns by FRP Wraps
FRP improve the confinement of the RC columns leading to:
Improving Axial Capacity
Buckling Resistance
Bomb Blast Resistance
